Much as I hate to admit it, and much as I regard the vast majority of people pushing the “Internet makes us dumber” line as vacuous douchebags, this seems about right.
Addendum: A commenter objects that the Internet is not displacing more “worthy” activities (reading Proust, socializing) but merely providing a new way to do these things. Lest there be any unclarity, my agreement is not some paper-fetishism about the superiority of hardbacks to ebooks. What I do think is true is that the very vastness of options the Internet brings together can make it hard—makes it harder for someone like me, anyway—to sustain focus on any one thing. I find it a lot harder these days to just sit for an hour with a book—pixel or pulp—and just focus on it for a hour straight. And I think part of that is attributable to the Net.